Disk usage report greater than effective lun size

[NEXYLAN_ROUBAIX]

Good morning everyone,

I'm having a weird issue with my FAS2020 running OnTap 7.3.6.

My volume 1 is 1,35TB.

System is reporting than this volume has only 221GB available (1116 MB used).

The thing is, I only have 2 lun created on this volume (200 + 500 GB). Snapshots are using 40 GB. Total : ~750GB used.

So, I was wondering where are the missing ~400GB ?

Am I missing something?

Thanks for your help,

GAëtan

[NEXYLAN_ROUBAIX]

fs1101> df -h

Filesystem               total       used      avail capacity  Mounted on

/vol/vol0/              8755MB      640MB     8114MB       7%  /vol/vol0/

/vol/vol0/.snapshot      460MB      152MB      308MB      33%  /vol/vol0/.snapshot

/vol/vol1/              1382GB     1161GB      220GB      84%  /vol/vol1/

/vol/vol1/.snapshot      153GB       43GB      110GB      28%  /vol/vol1/.snapshot

fs1101> df -Ah

Aggregate                total       used      avail capacity 

aggr1                   2093GB     1555GB      538GB      74% 

aggr1/.snapshot          110GB       87GB       22GB      79% 

fs1101> aggr show_space -h

Aggregate 'aggr1'

    Total space    WAFL reserve    Snap reserve    Usable space       BSR NVLOG           A-SIS

         2449GB           244GB           110GB          2093GB             0KB             0KB

Space allocated to volumes in the aggregate

Volume                          Allocated            Used       Guarantee

vol0                                 10GB           887MB          volume

vol1                               1544GB           520GB          volume

Aggregate                       Allocated            Used           Avail

Total space                        1555GB           521GB           538GB

Snap reserve                        110GB            87GB            22GB

WAFL reserve                        244GB            24GB           220GB

fs1101> aggr status

           Aggr State           Status            Options

          aggr1 online          raid4, aggr       root

fs1101> vol status

         Volume State           Status            Options

           vol0 online          raid4, flex       root, create_ucode=on

           vol1 online          raid4, flex       no_atime_update=on,

                                                  create_ucode=on

[aborzenkov]

Which volume is it (vol0 or vol1)?

I asked for “df -r” output which you did not show.

[aborzenkov]

Please show output of “df -rh” for this volume.

[NEXYLAN_ROUBAIX]

Hello aborzenkov,

This is vol1.

Output of df -rh :

fs1101> df -rh

Filesystem               total       used      avail   reserved  Mounted on

/vol/vol0/              8755MB      640MB     8114MB        0MB  /vol/vol0/

/vol/vol0/.snapshot      460MB      153MB      307MB        0MB  /vol/vol0/.snapshot

/vol/vol1/              1536GB     1217GB      318GB      463GB  /vol/vol1/

/vol/vol1/.snapshot        0GB       51GB        0GB        0GB  /vol/vol1/.snapshot

Yesterday, I changed reserved snapshot space to 0%. But no luck.

Gaëtan

[aborzenkov]

463GB is reserved for LUN overwrites due to fractional_reserve volume setting. This is done to protect you from out-of-space condition on LUNs. Please, read TR-3483 (or TR-3965 that includes 8.1) that describes in details how NetApp manages space in case of LUN.

[NEXYLAN_ROUBAIX]

Thanks for the tip aborzenkov !

What happens if I disable "Space Reserved" for this lun. What could happen?

Gaëtan

[aborzenkov]

You may run out of space on the volume, so that host write to LUN fails. As hosts normally do not expect hard disks to run out of space, they do not handle it gracefully.

Default settings on NetApp ensure, that there is always space for new write to LUN, so it behaves exactly as conventional disk.

[NEXYLAN_ROUBAIX]

What I don't understand is, why would a host require to write beyond my lun configured limit?

I created a 500GB lun on vol1 which is used by XenServer. XenServer know it has 500 GB available and not more.

In what case(s) would the "space reserve" be used?

Thanks,

Gaëtan

[aborzenkov]

Have you read TR-3483?